B cell-depletion therapies in humans as well as accumulating evidence from animal models indicate that B lymphocytes help initiate several autoimmune disorders including arthritis, lupus, and type 1 diabetes. Recent clinical trials have shown that restricting lymphocyte migration can ameliorate autoimmune diseases, raising the possibility that B cell circulation can be targeted as a means of treating auto reactivity. A major barrier towards achieving this goal is the dearth of mechanistic knowledge concerning the regulation of B cell homing receptors. This R21 project is predicated on the applicant's discovery that Kruppel-like factor 2 (Klf2) is a key transcription factor that controls mature B cel migration patterns. Moreover, Klf2 excision within the B cell compartment results in a lupus-like form of autoimmunity that further supports the link between altered B cell migration and disease progression. The premise of the current grant proposal is that Klf2 controls several important homing receptors and that by defining the genes and proteins that interface with Klf2, the molecular mechanisms that orchestrate B cell trafficking will be revealed. To achieve this goal, Aim 1 studies will initially use quantitative mass-spectrometry (MS) techniques to identify interactive proteins that facilitate Klf2 function. Parallel MS studies will define the protein complexes bound to the promoter regions of Klf2-regulated homing receptors. Together, these experiments will reveal a subset of Klf2-interactive proteins that directly shape B cell migration in a linage-specific manner. In Aim 2 studies, genes under Klf2 control that regulate B cell trafficking will be captured using a combination of DNA microarrays and chromatin immunoprecipitation followed by high-throughput DNA sequencing (ChIP-Seq) approaches. These results will define the genetic footprint of Klf2 and thus provide a cache of molecular targets involved in B cell homeostasis and self- tolerance. Access to primary B cell lineages that lack Klf2 provide the ideal control for the proposed biochemical and genetic experiments. Overall results emerging from the proposed project will provide the first insight into how mature B cell circulation patterns are maintained. In turn, these discoveries may promote the rationale design of new therapies to control B cell trafficking as a means of ameliorating disease.